A new type of magnetic servo amplifier

This paper describes a new 2-stage magnetic amplifier for high-performance servomechanisms, particularly to be used in connection with those types of 2-phase induction motors having such a low ratio of effective viscous friction to inertia that it is difficult to stabilize at high gain in a closed loop. The basic idea consists in feeding the amplifier field winding of the a-c reversible motor by a variable unidirectional current having a fundamental frequency (60 or 400 cycle) component and a d-c component producing an effective dynamic braking of the motor, preferably in such a way that the d-c component increases when the a-c component decreases, and vice versa.